<!DOCTYPE html>
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<head>
    <meta charset="UTF-8">
    <title>+</title>
    <script type="text/javascript">
        var var_01=1+1+'1';
        console.log(typeof var_01,var_01);
        var var_02='1'+1+2;
        console.log(typeof var_02,var_02);
        var var_03=+'213';
        console.log(typeof var_03,var_03);
        var var_04=+'asd';
        console.log(typeof var_04,var_04);
        console.log(typeof 1,typeof (1+''));
        console.log(typeof true,typeof (true+''));
        console.log(typeof null,typeof (null+''));
        console.log(typeof undefined,typeof (undefined+''));
    </script>
</head>
<body>

</body>
</html>